With the increased recording density of magnetic disks, the distance between a magnetic disk serving as a recording medium and a head for recording and reproducing information has become almost nil as they approach coming into contact with each other. The magnetic disk surface is provided with a carbon protective, film and a lubricant film to diminish abrasion caused by contact with the head or sliding of the head thereon, and to prevent contamination of the disk surface. The carbon protective film is typically formed by sputtering or CVD. The disk surface is protected by two films, i.e., the carbon protective film and the lubricant film provided thereover. In particular, the lubricant layer provided on the top must have various properties, such as long-term stability, chemical resistance, friction properties, and heat resistance.
Conventionally used lubricants for magnetic disks are fluoropolyethers having functional groups, such as hydroxyl and amino, at their molecular terminals. However, fluoropolyether-based lubricants have low durability against Lewis acids. When the lubricants come into contact with the magnetic head, their backbone is cleaved by alumina (Al2O3; contained in a magnetic head component, whereby the lubricants become lower molecules, ultimately dissipating from the magnetic disk surface. Thus, the film formed by such lubricants cannot be maintained in a system where the magnetic head comes into contact with the magnetic disk or slides on the magnetic disk,
A recent rapid increase in the information recording density of magnetic disks requires a reduction in magnetic spacing between the magnetic head and the recording layer of the magnetic disk. It is thus becoming important to further reduce the thickness of the lubricant layer present between the magnetic head and the recording layer of the magnetic disk.
In response to this need, fluoropolyether-based lubricants have been proposed which have functional groups at their molecular terminals and in the middle of the molecular chains (e.g., Patent Documents 1 to 4). Patent Document 1 teaches that the use of a lubricant having hydroxyl both in the molecular chain and at the molecular terminals reduces the thickness of one molecule even when the lubricant is highly polymerized. Patent Document 2 teaches that the use of a lubricant having hydroxyl at the molecular terminals and in the center of the molecular chain, optionally with an aromatic ring in the center of the molecular chain, reduces the thickness of a lubricant layer while enabling high film coverage. Patent Document 3 teaches that the use of a compound having an aromatic ring at the molecular terminals and in the center of the molecular chain can improve the heat resistance. Patent Document 4 teaches that the use of a lubricant having hydroxyl at the molecular terminals and a benzene ring in the center of the molecular chain reduces the thickness of one molecule to thereby reduce the spacing between the head and the disk, thus enabling durability against sliding.
However, neither of Patent Documents 1 to 4 discloses a lubricant that can reduce the thickness of one molecule to thereby reduce the spacing between the magnetic head and the magnetic disk, while being resistant to decomposition by alumina when coming into contact with the magnetic head.